The present invention relates generally to information recording and/or reproducing systems; more particularly it relates to improved strobing methods and means adapted for magnetic recording and detection systems.
The present invention will be understood as commonly useful with magnetic disk recording and reproducing systems wherein one or more read/write heads are employed for data storage. Such systems are typically employed to provide auxiliary data storage in an automatic data processing system--with the data being recorded on the concentric circumferential tracks about a disk.
Particulars of a preferred disk drive system and associated servo apparatus and data encoding may be found in copending U.S. patent application Ser. No. 847,012 filed on Oct. 31, 1977, now U.S. Pat. No. 4,149,200 by Daniel Card and commonly assigned herewith. This application is incorporated herein by reference. One purpose of this case is to teach improved strobing for a read/write arrangement used in a high performance, high capacity, low cost (per megabyte) recording equipment.
Workers will appreciate that such equipment presents certain problems, especially when implemented with a servo data format technique like that of the cited application (i.e., "embedded servo" data). In such instances, one must typically resort to using transducer core gaps which are relatively narrow. This, in turn, introducers such problems as reduced "read-signal amplitude" (and a lower signal/noise ratio), increased "adjacent track interference" and increased error from read-data decoding.
Also, "track overhead" is likely increased, requiring higher bit density (bpi). This, in turn, leads to pulse crowding which causes further reduction in read-signal amplitude (and in signal/noise), as well as increased peak shift. This invention is intended to alleviate such problems in an improved strobe arrangement.
Workers in the art are familiar with various methods for (coarse and fine) servo positioning--such as the methods described in the cited application. For instance, workers have used specially selected servo encoding patterns recorded along servo-sector portions of each track to indicate coarse and fine positioning signals. Each such servo sector may contain a servo code including: a common reference transition, followed by "track-follow" servo data (e.g., for providing fine positioning with respect to two adjacent tracks); this followed by "track-seek" servo data to control coarse positioning of the transducer head. The present invention will be seen as apt for combination with such an ("embedded") servo format (e.g., see U.S. Pat. No. 4,027,338 to Kril)--as opposed to a "dedicated" (sector or track) format. Workers will appreciate that an "embedded" format presents certain problems, since track density and/or bit density are increased. This invention addresses those problems.
More particularly, the instant features will be seen as especially apt for use with a certain servo data format (see cited application). In this format, the fine servo data which comprises a "reference transition" followed by another opposite polarity transition at either a first or second position of each track depending on whether the track is odd or even--thus recording an odd or even indicium at respective different relative located positions on adjacent tracks. And, in such a format, the "coarse" servo data comprises a track-group identification code in a series of successive data cells, each cell containing a single magnetic transition representing either a binary "0" or "1" depending on whether the transition occurs in the first or second half of the cell. Preferably, this "course" pattern employs a specially chosen sequence, such as a Gray code sequence, permitting only one change in the (magnetic transition) code between adjacent tracks. Also, such a code is preferably laid-down and manipulated so that a "between track" condition is readily detectable, and results in detected pulses being obtained in both the first and second portions of the "changed cell".
Workers will understand that preferred embodiments of this invention will provide a high performance, high capacity, low cost (per megabyte unit) system; one able, for instance, to increase the data capacity of a conventional disk storage system. Workers will also appreciate that these advantages are achieved using relatively conventional, readily available subsystems. For instance, disk systems improved by the taught features will be seen to provide a very high density of useable bits (for a record with a "several hundred megabyte" capacity, the order of several megabytes, or more, per square inch is feasible, for example)--preferably in a relatively compact low-cost configuration (e.g., of one to two dozen cubic feet, costing just a few dollars per megabyte), along with very reasonable access-to-data times (e.g., the order of about three dozen ms.).